1. Field of the Invention
The present invention relates to a common inversion driving type liquid crystal display (LCD) device and its driving method.
2. Description of the Related Art
Generally, an LCD apparatus is constructed by an amorphous silicon panel including a plurality of signal lines (or data lines) arranged along a column direction, a plurality of scan lines (or gate lines) arranged along a row direction, a plurality of active pixel units each including one thin film transistor (TFT) made of amorphous silicon and one pixel capacitor located at intersections between the signal lines and the scan lines, a signal line driver formed on a flexible printed board called a tape carrier package (TCP) connected to the panel, and a scan line driver formed on another flexible printed board (TCP) connected to the panel. However, as the capacity of the panel has been increased, it is difficult to connect the signal line driver and the scan line driver to the panel due to the narrow pitch of the scan lines and the signal lines.
Recently, TFTs made of polycrystalline silicon formed on a glass substrate by a low-temperature chemical vapor deposition (CVD) process have been used in the above-mentioned panel, so that the entire or part of a signal line driver and a scan line driver can be introduced into the panel. Thus, it is easy to connect the signal line driver and the scan line driver to the panel, or it is unnecessary to connect the signal line driver and the scan line driver to the panel. In this case, however, the glass substrate of the panel becomes very large, which would increase the manufacturing cost and decrease the reliability.
A first prior art LCD apparatus (see: JP-2001-109435-A) is constructed by a polycrystalline silicon panel including a plurality of signal lines, a plurality of scan lines, a plurality of active pixel units located at intersections between the signal lines and the scan lines and a scan line driver by using polycrystalline silicon formed on a glass substrate by a low-temperature CVD process, and a signal line driver formed on a flexible printed board (TCP). Also, the first prior art LCD apparatus is constructed by a selector circuit connected between the signal line driver and the amorphous silicon panel to time-divisionally connect the signal line driver to the signal lines. In this case, the selector circuit is formed in the polycrystalline silicon panel, so that the number of connections between the signal line driver (TCP) and the polycrystalline silicon panel is decreased. Thus, it is easy to connect the signal line driver to the polycrystalline silicon panel. This will be explained later in detail.
A second prior art LCD apparatus (see: JP-2001-337657-A) is constructed by a polycrystalline silicon panel including a plurality of signal lines, a plurality of scan lines, a plurality of active pixel units located at intersections between the signal lines and the scan lines, a signal line driver and a scan line driver by using polycrystalline silicon formed on a glass substrate by a low-temperature CVD process. Also, the second prior art LCD apparatus is constructed by a selector circuit connected between the signal line driver and the polycrystalline silicon panel to time-divisionally connect the signal line driver to the signal lines. In this case, the selector circuit is formed in the polycrystalline silicon panel, so that the signal line driver is decreased in size. This will be explained later in detail.
On the other hand, in order to avoid a so-called residual image phenomenon, the polarity of voltages at the signal lines is inverted with respect to the voltage at a common electrode for every frame, which is called a frame inversion driving method. Also, in order to avoid the flicker due to the frame inversion driving method, a horizontal inversion driving method, a vertical inversion driving method or a dot inversion driving method is carried out. In the horizontal line inversion driving method, the polarities of voltages at the signal lines are inverted with respect to the voltage at the common electrode for every scan line. Also, in the vertical line inversion driving method, the polarities of voltages at the signal lines are inverted with respect to the voltage at the common electrode for every signal line. Further, in the dot inversion driving method, the polarities of voltages at the signal lines are inverted for every dot (video signal). However, the amplitude of the voltages at the signal lines in the frame, horizontal, vertical and dot inversion driving methods is twice that in a non-inversion driving method, which requires higher breakdown characteristics of the signal line driver. In order to decrease the amplitude of the voltages at the signal lines in the frame, horizontal, vertical and dot inversion driving methods, a common inversion driving method is adopted to invert the polarity of the voltage at the common electrode in synchronization with the inversion timings of the frame, horizontal, vertical and dot inversion driving methods.
When the common inversion driving method as well as at least one of the frame, horizontal, vertical and dot inversion driving methods is applied to the above-mentioned first and second prior art LCD apparatuses, since the voltage at the common electrode has a transient phenomenon, the difference in voltage between the signal lines time-divisionally driven by the signal line driver and the common electrode is affected by the transient phenomenon of the voltage at the common electrode.